A quarter-century after his ground-breaking Sandman comic was launched, Neil Gaiman is returning to the character that made him famous with a six-issue prequel about Morpheus, the Lord of Dreams.

Gaiman – currently basking in the glory of phenomenal reviews and booming sales for his first adult novel in eight years, The Ocean at the End of the Lane – has penned a limited series that tells a new story about the much-loved character he created for DC comics in 1988 and which ran for 75 issues.

Sandman was initially published as part of the main DC comics line but in 1993 was incorporated into the publisher's new Vertigo imprint which offered edgier, more adult comics. The first issue introduced Morpheus, or Dream, one of the immortal siblings known as the Endless. The ruler of a kingdom known as the Dreaming, the character was an instant hit, and when Gaiman introduced Dream's sister Death as a cocksure goth girl he won over a legion of fans seemingly for ever.

This October sees the first issue of the new comic, Sandman: Overture, produced with artist JH Williams III, 25 years since the first issue of Sandman (it had a January 1989 cover date but was published in October 1988).

The storyline describes what happened to Dream before the events of the first ever comic, in which he was imprisoned by an Aleister Crowley-ish Satanist, Roderick Burgess, in the cellar of his tumbledown English mansion at Wych Cross.

Gaiman said: "This is the one story that we never got to tell. In Sandman #1 Morpheus is captured somehow. Later on in the series, you learn he was returning from somewhere far, far away – but we never got to the story of what he was doing and what had happened. This is our chance to tell that story, and JH Williams III is drawing it. It's the most beautiful thing in the world."

DC is making this "literary event" last a year by releasing the issues of Sandman: Overture every two months. And, perhaps learning from Headline's £250 deluxe edition of Ocean at the End of the Lane that Gaiman fans have deep pockets, DC will also publish Sandman: Overture special editions in the fallow months when the main comic is not out, featuring Gaiman's original scripts, additional concept art and extra text features.

The impact of Sandman on the comics world and popular culture in general cannot be overestimated, with DC pointing out that it "stands tall as one of the few graphic novel series ever to be on the the New York Times Best Seller list." Stephen King said of the Sandman comics, "These are great stories, and we're lucky to have them", while Norman Mailer called it "a comic strip for intellectuals".

Given the huge love for Sandman, it could be seen as something of a gamble to revisit a character and series that had such critical acclaim so long ago. Is Gaiman at all worried about the reception the prequel will get? He says: "It was (and is) both nerve-wracking and fun. I definitely feel like the world is looking over my shoulder at what I'm writing."

More details about the new series will be released at San Diego Comic Con, the biggest comics convention in the world, which takes place from July 18-21. These days it regularly attracts big Hollywood names as well as comics stars, and it has now become traditional for publishers to make big announcements there. Gaiman, JH Williams III and British artist Dave McKean, who created the stunning collage-effect covers for the entire run of the first Sandman series, will be in attendance, as will Sam Kieth, the artist who drew the first five issues of the Sandman comic. Sandman is going to be something of the star of the show, gracing the official convention souvenir booklet and T-shirts.